The present invention relates to the field of X-Y Tables for plotters, automatic drafting tables, positioning devices for workpieces such as printed circuit boards, laser systems, optical systems, and the like.
The more usual construction of X-Y Tables includes constructing a positioner assembly for the X axis and thereafter constructing an additional positioner assembly such that its slider will move in the Y direction generally perpendicular to the X direction where the former is built upon the latter. Such superpositioning of the X and Y positioning devices results in a system having a relatively large thickness. Moreover, the transfer of the vertical (Z direction) load of the workpiece to the base plate is through the bearing surfaces of both superposed Y and X positioning devices, and the result is that deflections and sags in the Z direction alter the true position of the workpiece relative to its theoretical position and increases the drag forces. U.S. Pat. No. 3,743,904 to Weisler et al. discloses an X-Y positioning device for eliminating the vertical stacking of the positioners by locating them in the same plane and transferring the weight of the workpiece to the base plate through four support blocks at the four corners of the top plate. This system however, as built and sold, suffers from the fact that the X motion moves the top plate in the X direction but generates deflections of the Y positioner in the horizontal plane due to the resulting cantilever loads, and thus the true position measurement is still inaccurate; also the extent of motion is limited; also the load creates sag in the top plate; also the system does not allow for a central access area below the top plate.
It is thus an object of the present invention to provide a novel X-Y positioning device which is shallow, simple in construction, very accurate and yet may be constructed to provide very large displacements of the workpiece in both the X and Y directions.
It is a further object of the present invention to provide a simple shallow X-Y positioning device which may transfer the vertical load, generally the weight of the workpiece but may include impact or other vertical forces upon the workpiece, directly from the top workpiece support plate above the positioning mechanisms to the base plate, bypassing completely the vertical loading of the bearings and bearing surfaces to thereby eliminate much of the cross influence of the axes upon each other. The vertical forces can also be transferred directly to the base plate via a stationary anvil-like device situated below the workpiece, if the application calls for this anvil-like device.
It is a further object of the invention to provide a simple and reliable X-Y positioning system having both X and Y drive devices essentially in the same plane and having the drive motors stationary relative to the base plate, thus decreasing the number of moving parts, moving electrical cables, moving fluid conduits, and undesired mass adding to the weight of the workpiece.